Processing of heavy gas oils



Fe 8, 1944. E. HEMMINGER 2.341.316

PROCESSING OF HEAVY GAS OILS F1106 Mil. 17, 1940 cn TA Y we GOMVGM my r r Irv-BIO can raw 5' Mwr Patented Feb. 8, 1944 UNITED STATES PATENT OFFICE 3. Claims.

point. In the thermal cracking of gas oil, it is not practical, or, at least there are serious disadvantagesin treating a gas oil having a boiling range extending substantially above 700 F. These disadvantages are: (1) In a vapor phase thermal cracking operation where 25% of the feed stock boils above say 700 R, such excessive amounts of coke are formed in a short-time as to render the process entirely non-feasible commercially; and (2) in liquid phase thermal cracking, regardless of the boiling range of the feed stock, the gasoline produced has a low octane rating.

One object of this present invention. is to transform chemically a gas oil of which about 95% boils above 700 F. in the presence of ,a cracking catalyst such as an acid treated clay, under conditions such that a relatively small amount of hydrocarbons boiling within the gasoline range are produced and wherein the product primarily produced is a gas oil boiling substantially within the range offrom about 400 F. to 700 F. The gas oil thus produced after separation from gasoline and from the normally gaseous constituents, may be used as a heating oil or may be conveniently and with certain advantages cracked in vapor phase toproduce gasoline of high octane rating.

Another object of my invention is to convert a gas oil boiling within the range of from about 700 F. to 1050 F. to a gas oil boiling within the range of from about 400 F. to 700 R, which lat-- ter gas oil is a satisfactory cracking feed stock for a liquid phase cracking operation, where a high octane rating gasoline is not desired, since the lower boiling gas oil gives much higher conversions to gasoline per passage through the cracking operation, as well as higher yields of gasoline, than the higher boiling range gas oil.

Another object of the present invention involves hydrogenating a gas oil fraction boiling within the range of from about 400 F. to 700 F. produced catalytically from a gas oil of higher boiling'range to improve its quality as a thermal cracking stock.

Other and further objects of my invention will appear from the. following more detailed description.

To the-accomplishment of the foregoing and related ends, I provide a process and a suitable apparatus for carrying out the. said process, in which, .argas oil of relatively high boiling range is catalytica-lly treated to produce a gas oil of relatively lower boiling range, and, in particular, being rich in fractions boiling below 700 F.,and, if desired, thereafter subjecting the formed gas oil to hydrogenation followed by thermal cracking to produce gasoline, or'the gas oil produced may be employed as a :heatingoil.

My invention will be best understood by setting forth a concrete example and the manner in which it maybe carried out.

In the drawing, the single figure represents. diagrammatically a suitable apparatus in which myprocessmaybe carriedout.

Referring to the accompanying drawing in detail, a gas oilboiling in the range of from about 700 F. to 1050 F. is introduced into the system through line I and thence dischargedinto the .pump .2, thereafter fed intoa fired coil 3 disposed in ,a. turnace setting 4. In the coil v3, the gas .oil is heated to a temperature of about800 F. to 950 whereupon it is discharged into tar separator 6 where, in the presence of steam .or other diluents, the larger portion of the oil is vaporizedleaving about 3% to 10% pitch or tar based on the charging stock to. be removed through line 8, the vapors discharging through line 7 into a catalytic conversion chamber 9 containing preferably a plurality of spaced apart beds of catalytic material such as an .acid treated clay, th said beds. being supported on, foraminous trays T ,,v I 1 :3,. and .'l4. The v p rized. hydrocarbons pass in series through the several trays of catalyst and are then withdrawn overhead through. line [0, The shell of chamber 9 is preferably lagged with heat insulating material, and the temperature. of. the vapors entering the said chamber is preferably sufliciently high so that the heat. loss caused by the endothermic nature of the cracking operation will not cause. a temperature drop in the uppermost tray Tl below that at which active cracking may occur. .Ordinarilman inlet'temperature to the chamber 9 of 850 F. 'to'925 F. gives best results. The pressure. existing, in chamber 9 may be from 1-10 atmospheres, but best results are obtained by operating at about 10 lbs. per square inch gauge. The linear velocity of the oil vapors passing through the catalyst is sufiiciently high so that only 5% to 15% gasoline by volume, based on the F. which is withdrawn through line l8. In addi-v tion to gas oil withdrawn through line I8, a heavy gas oil boiling in the range of from about 700 F. to 900 F. is withdrawn through line l9, but this fraction usually contains tar and aromatics and preferably is rejected from the system. A light gas oil, say a cut boiling within 43. The fraction withdrawn through line 38 represents an unconverted gas oil, and this oil may be recycled to line I for further catalytic treatment or passed through line 39 to line 28 for further thermal treatment in cracking coil 30. As an alternative procedure, I may discharge the gas oil through pipe I 8 directly into coil 30 through lines 50 and 29 thus by-passing the hydrogenation step. Also I may remove gas oil in line I8 from the system through draw-off pipe 5|.

Some of the obvious modifications of my process include employing a powdered catalyst suspended in the gas oil during the cracking of the charging the relatively narrow range of from about 400 F. to 500 F. may be withdrawn through line and this cut may be used for any desired purpose. Preferably, however, all of the gas oil, except the bottoms withdrawn through I9, is withdrawn through conduit |8. A gasoline fraction is withdrawn from tower I4 through line l0, and normally gaseous hydrocarbons'are withdrawn through line H. The total amount of permanent gases and gasoline should not amount to more than 20% by weight of the original charging stock.' The gasoline produced may be refined, stabilized and sent to storage in equipment not shown. I

The gas oil fraction is preferably delivered through conduit l8, to a hydrogenation unit 2| where it contacts hydrogen delivered to the hydrogenation unit from some available means through conduit 22, and a suitable hydrogenation catalyst. The hydrogenation of the gas oil is 'preferablycarried out at a temperature of about 700 F. to 900 F. and under a pressure of 0 to 200 atmospheres in the presence of a catalyst such as a mixture of equal parts by weight of nickel sulfide and tungsten sulfide, the amount of hydrogen being from about 12,000 to 15,000 cubic feet of hydrogen measured under standard cor'1ditions,per barrel of gas oil feed to the system. The feed rate of gas oil is preferably from 1 to2 volumes of cold oil per volume of reactor per hour. The hydrogenated oil is then withdrawn from the hydrogenation unit through line and passed into separator 21 where the hydrogen isseparated from the oil and recycled through line 24 to line 22. The gas oil is withdrawnfrom separator 21, through conduit 28 carrying pressure reducing valve 29 and thence forced into fired coil 30. I

In the coil the gas oil is heated to a temperature of from about 850 F. to 1050 F; while under a mild pressure, say 10 to 20 lbs. per square inch gauge pressure, whereupon the cracked product is delivered through conduit 3| to tar separator 32 where tar is withdrawn through pipe 33 while the vapors pass overhead through conduit 34 to a fra'ctionatin'g column 35. In this column, the

oil is fractionated to yield a gasoline fraction stock. -Thus powdered catalyst may be dispersed or suspended in the vapors in line and conducted to a reaction zone maintained under the same or similar conditions as hereinbefore set forth in connection with the description of the operation carried out in reactor 9. Of course,-in this modification tray type reactor 9 would be replaced by a coil or a drum. Also I may use instead of acid treated clay, a catalyst composed of silica, alumina gels, mixtures or compositions, or I mayuse silica gel mixed with magnesium oxide gel."

While I have described a process hereinbefore which includes hydrogenation of the gas oil produced catalytically, followed by thermal cracking to form gasoline, I wish to point out that my invention is not limited to the said process but in its broadest aspect my process involves converting a heavy gas oil say one boiling in the range of from about 700 F. to 900 F. or1050 F. to a gas oil boiling from about 400 F. to 700 F. which may be used for any purpose, i. e. as a cracking stock in a gasoline producing operation or as a heating oil. Numerous modifications of my invention will be readily understood by those skilled in this particular art.

What I claim is: I 1. The method of preparing a lower boiling gas oil particularly suitable for thermal cracking from a higher boiling gas oil comprising at least oi. hydrocarbons boiling above 700 F. and below 1,050 E, which comprises heating the higher boiling gas oil to a temperature between 800 and 950 F., introducing the heated gas oil into a tar separator wherein the major proportion of the gas oil is vaporized, subjecting the vapors so obtained to catalyticcracking in a reaction zone in which they are resident for about 2 to 30 seconds, to produce between 5 and 15% by volume of gasoline based on the, gas oil, and recovering from the products of catalytic cracking a fraction boiling between 400 and 700 F.

2. Process according to claim 1 in which the fraction boiling between 400 and 700 F. segregated from the products of catalytic cracking is subjected to non-destructive hydrogenation, the hydrogenated product is fractionated to produce a gasoline fraction and a heavier fraction-and a heavier fraction is returned to the stage in which the higher boiling gas oil is heated. 1

3. Process according to claim 1, in which the products from the catalytic cracking step include a gas oil of boiling range between 400 and 500 F., and the total amount of permanent gases and gasoline produced in the catalytic cracking step do not exceed 20% by weight of the higherboiling gas oil.

CHARLES E. HEMMINGER. I 

